The way we categorize problems is by using the built-in MediaWiki categories. For instance, one category is "sorting." If we want to mark a problem as being sorting related, we include at the bottom of the page:

[[Category:Sorting]]

Note, case DOES matter, and we use standard title case for all categories. Feel free to tag a problem with as many categories as you like.

After you've sorted a problem, give yourself credit! Within the {{problem}} template included on each problem page, there is an attribute called "sorter." When you categorize this problem, put your username in the attribute. For instance, the problem template should look like this: